Firefighters in California said they have a special weapon in their battle against a massive wildfire, an unmanned military Predator drone similar to those used in Afghanistan.

Authorities said they are using the unmanned aircraft to provide information on any new fires they would otherwise not be able to see. The U.S. Forest Service said the so-called Rim Fire has swelled to about 780 square kilometers.

More than 4,500 firefighters are battling the massive blaze, which has consumed about 78,000 hectares of land, including part of Yosemite National Park. The U.S. Forest Service said firefighters have contained about 30 percent of the Rim Fire and expect to fully contain it by September 20.

Their efforts have been hampered by strong winds, high temperatures and inaccessible steep terrain.

The massive fire has destroyed more than 100 homes, businesses and other structures. Authorities said about 4,500 other structures are threatened by the blaze.

Mandatory evacuations are in place in at least two areas.

The cause of the fire that broke out August 17 is under investigation. It is one of dozens of large wildfires burning in the western United States, which has been plagued by a lack of snow and rainfall this year.